1. Field of the Invention
This invention is directed to solenoids, in general, and to an improved solenoid which is adaptable to operate the valves in most irrigation systems by means of a versatile, yet simple, adjustment to the novel plunger thereof, in particular.
2. Prior Art
A wide variety of irrigation systems and other fluid control systems are known. These systems usually contain valves which are opened and closed by means of a solenoid, thereby controlling the flow or non-flow of water or other fluids. The valves of the existing systems have fluid constantly being delivered by pipes or other usual means. The solenoid controlled valve is positioned at a desired place in the fluid flow pattern such that it is able to stop or permit the fluid flow selectively. Typically, the solenoid includes a coil and a plunger which is controlled by signals supplied to the coil. The signals are supplied by a control panel which is usually remote from the solenoid. Normally, a signal is supplied to the solenoid to move the plunger relative to the coil. Movement of the plunger operates to control the valve in the irrigation system. When the coil within the solenoid is activated, the plunger, typically, is pulled into the solenoid toward the coil by the electromagnetic force produced at the coil. Typically, this operation moves the plunger off the solenoid discharge port within the valve, thereby permitting the water pressure to force the valve open. When the signal to the coil ceases, the plunger is pushed by a spring to a position extended from the solenoid. In this extended position, the plunger blocks the fluid flow by moving onto the solenoid discharge port, i.e., the valve is closed. Of course, whenever a solenoid ceases to function properly, the valve may be "frozen" shut and no fluid is delivered to the system. Conversely, the valve may remain in the open (or partially open) condition and constantly leak fluid. Neither of these arrangements is satisfactory and, usually, the only solution currently available is to replace the entire valve or, at least the entire solenoid in the valve.
When an irrigation system uses only one model of valve or solenoid, the replacement of a solenoid can be a relatively simple task, assuming the part is still available from the manufacturer. In more complex irrigation systems which have been installed over time and/or under the direction of several individuals, there is likely to be more than one type of equipment present. In both of these situations, replacing a solenoid can become a futile act of trying to find the matching manufacturer replacement. Some solenoids are difficult to obtain. Other solenoids are impossible to obtain because they are not longer manufactured. Those persons in charge of irrigation system may, therefore, find it necessary to keep a large and varied inventory of solenoids on hand to be able to promptly replace those which fail before the flora is damaged, the location is flooded, or the like.
Maintaining such an inventory of solenoids is not only costly, but requires much storage space and complex record keeping to maintain an adequate supply. Moreover, the inventory is, eventually, depleted and the problem of obtaining proper solenoids recurs.
One of the most irksome and expensive parts of the replacement process is the frustrating attempt to replace a solenoid even when large inventories are available. Typically, the irrigation specialist takes a dozen of the most likely types of solenoids into the field for repair and/or replacement. This inefficient operation can be even more exasperating if the specialist find that none of the units is appropriate. Now a return trip must be made to obtain the correct model of solenoid, assuming that it is even available. Then another service trip is made into the field to finally do the actual replacement work. Thus, the replacement process becomes even more expensive and time consuming.
The difficulty of the replacement process was somewhat reduced by the introduction of a solenoid which has three different height replacement plungers. This multiple-plunger solenoid is sold under the trademark SUPER MAX. (SUPER MAX is a trademark of National Irrigation Specialists of Anaheim, California). In this solenoid, a plurality of interchangeable plungers of different lengths is provided. To implement this system, a chart is provided with the SUPER MAX solenoid which keys each of the different plungers to specific irrigation systems.
While this solenoid was a vast improvement over the huge inventory method of solenoid preparedness, it is still cumbersome, requiring a chart and extensive parts inventory. For example, in any replacement at least two of the three plungers will be unnecessary.
In addition, the SUPER MAX solenoid is made to cover a broad spectrum of valves with only three fixed dimension plungers. The valve models produced by the different manufacturers vary slightly. In addition, the variations between different brands of irrigation systems frequently results in a less than perfect fit of these "general-fit" plungers. The nature of each plunger is to cover more than one type of valve and, therefore, is like the proverbial "Jack of all trades and master of none". The fit of the plunger is frequently good, but not perfect in many situations. For example, if the plunger is too short, the magnetic field within the body of the solenoid is unable to "capture" the plunger, pull it up and thereby open the valve. Conversely, if the plunger is too long, the valve is always closed because there is no space in which it may move toward the magnetic field and thereby open the valve.
Although solenoids of irrigation systems are discussed above, any fluid control system which includes the use of valves and electrically activated solenoids has comparable difficulties. There is clearly a need for a precisely fitted solenoid which will serve as a replacement in any irrigation or fluid control system. Such a solenoid will provide the additional benefits of reduced inventory and associated costs, lower labor costs because repeat trips to the field are unnecessary, and elimination of the problem of unavailable solenoid models.